I think they thought we were reviewing a book on how to make real LEGO guns. But that is not the case at all.

"Real lego guns"? I seriously doubt that there is any such thing. If what appears to be an innocuous video gets a strike you need to consider if it was something other than the actual video, such as misleading tags, or links to questionable sites. Exactly what did the message say, was it perhaps for "Spam or misleading content"?